The present invention relates to a pressure control valve, in particular a solenoid-operated valve for brake systems with slip control.
Conventional pressure control valves of this type find use in a wide variety of technical fields of application.
In the German printed and published patent application 32 40 276, a pressure-balanced pressure control valve of the aforementioned type is described. This pressure control valve is provided with a sealing ring inserted in a guide portion which seals a first chamber relative to a second pressure chamber as the clearance fit between the valve shaft and the guide portion is closed to gap leakage flows.
When looking more closely at the valve design, it becomes apparent that a satisfactory sealing effect is only guaranteed when a fit with tight tolerances between the valve shaft and the guide portion of the housing accommodating the sealing element is chosen. However, as miniaturization advances, the establishment of a clearance fit with tolerances that are as tight as possible reaches the limit of practicability in production, because of cost, production, and functional considerations. In addition, a clearance fit which is too tight impairs the capability of self-centering of the valve shaft relative to the valve seat which is required for a perfect valve closing function.
Furthermore, the use of elastomeric seals between the guide web of the housing and the valve shaft, which is known from the prior art, produces, inevitably, high frictional forces which accelerate wear and which must be compensated for by means of correspondingly increased spring forces and magnetic forces. Also, miniaturization of elastomeric seals is possible only to a very limited extent. In another arrangement disclosed in German printed and published patent application 32 40 276, a diaphragm seal, which is attached to the valve shaft and to the valve housing, is used instead of an annular seal. This alternative sealing measure at the valve shaft also is not sufficiently satisfactory in practical use since the radial mismatch required for the self-centering effect of the valve closure member can only be transmitted onto the diaphragm in a reduced way, in particular as the valve size is decreased.